OK guys. Serious question. At what low end temperature will blade steel experience decarb? Even a ittle? At draw back temps?
Background. I have been experimenting with different steels to calibrate my recipes to my oven. This requires me to harden, start low on the charts and multiple draw the blades till I see it perform to my satisfaction. Of course it also means I have the blade quite sharp (except perhaps a chip now and then)during the subsequent higher draw. Naturally, if the blade had chipped on a previous chop test, I would roll it again. In the event it does not chip but I test with a file and it still skates, I sometimes will raise the oven temp and draw again. In that situation, I have to re roll the edge anyway now because the edge is so soft, even the burr was floppy, if you know what I mean. Cant feel it with your finger tips. With just a smidge of material being removed, the edge is back nice and crisp and the burr stiffened up where it grabs you finger skin when you pull it backwards. You know.
Are any of you guys who do a lot of testing finding something along these lines?
Do you use the burr's behavior as an indicator, small as it may be, as part of your over all estimation of the blades condition?
Lin,
I can only speak from industrial side of things. Where I work we case harden 1010X in a carbon enriched environment (bring the case depth of the part to about .040 meaning the part has absorbed enough carbon about .95 percent carbon that it would harden properly). In some case we have to anneal the said parts back to a machinable hardness. I say this loosely. Our technique is not what I'd call an anneal. It calls for us to heat the parts to 1250 for an hour and let them set and cool slowly for 6 hrs. Having seen this and been around it 1250 is enough for carbon migration and decarb. After this process I've tested the case depth and it has grown to over .045 in depth and the surface will got get as hard meaning we've had some decarb.
The only question I have is after you've tested your edge and it did not preform well, did you after a subsequent draw remove more material and make the edge thicker, hence building up the edge and removing the previous decarb area. Saying that, did you created a thicker area at where you originally hted and removed the problem. This would lead into how thick was your edge at ht. I'd say you'd would need at least .030 on each side before heat treat and maintain that at each tempering cycle to have a true and fair test.
Does this make sense.
Dave from Diller
Thanks David. Yes it makes sense. That would be a more accurate situation.
My heat treat grind is pretty consistant and I expect a little decarb at the hardening, but most of the time it goes away the first time I roll the edge. In another thread I mentioned that sometimes I forge too close and end up having to back into the blade edge a little to reach the hard stuff. I usually grind the geometry a little thin when I test the edge, trying to find the edge's failing point and, considering all factors, will go from there depending on the nature of the failure.
I've come to notice that the burr will behave pretty consistantly when the heat treat (the grind too, but especially the HT)is correct. When the burr behaves weird, I start checking other things. It certainly is not the only thing I go by but its just an indicator. The angle of grind affects the burr too, so its all part of a bigger picture.
A sharp file is the main thing I use to determine the edge's degree of hardness. I drew the blade back, rolled and edge, tested and it showed to be too hard by the file, so I raised the temp 15 degrees and drew it again. Now with that small increase in temp, the edge showed too soft for my estimation of what it should be. I re rolled the edge and it started acting beter, even the file showed it harder. That prompts my question.
I appreciate the information Dave. I would also like to hear about more anecdotal findings as well as hear from those who have similar questions pertaining to the subject.
